Geometric effect promoted hydrotalcites catalysts towards aldol condensation reaction

Abstract

In solid basic catalysis field, how to achieve optimized activity and desired stability through elaborate control over basic site properties remains a challenge. In this work, taking advantage of the structure memory effect of layered double hydroxides (LDHs), rehydrated Ca4Al1-xGax-LDHs and Ca4Al1-xInx-LDHs catalysts were prepared and applied in aldol condensation reaction that isobutyraldehyde (IBD) reacts with formaldehyde (FA) to obtain hydroxypivalaldehyde (HPA). Notably, the resulting re-Ca4Al0.90Ga0.10-LDHs exhibits an extraordinarily-high catalytic activity (HPA yield: 72%), which is to our best knowledge the highest level in this reaction. The weak Brönsted basic site, 7-coordinated Ca-OH group, which serves as an active site, catalyzes the condensation process and promotes the product desorption. Studies on structure-property correlations demonstrate that Ga as a structural promoter induces a moderate expansion of the laminate lattice, which results in a significant increase in the concentration of weak basic sites in re-Ca4Al0.90Ga0.10-LDHs, accounting for its high catalytic activity. This work illuminates that geometric structure of basic active sites can be tuned via introducing catalyst additive, which leads to a largely improved performance of hydrotalcite solid basic catalysts towards aldol condensation reaction.